Demands for grains are increasing because of a decrease in production due to draught and the like in wheat production regions caused by worldwide abnormal weather in recent years, embargos involved in the decrease in production, use thereof as biofuels, and the like. Consequently, price of sales to flour milling companies of imported wheat purchased by the government is continuously rising.
It is anticipated that food shortages on a global scale will be caused by the increase in the world population and prices of foods including wheat will further increase.
Therefore, the food shortages and the price rises are critical problems for Japan that has a low food self-sufficiency rate and depends on import for most of wheat.
On the other hand, in Japan, along with the change in dietary life, people further shift away from eating rice, rice consumption. And the consumption of cooked rice tends to decrease year after year.
Therefore, it is anticipated that a demand for rice flour as an alternative to wheat flour will further expand in future.
Rice flour has been produced by various methods from long ago. Specific methods for the production of rice flour include a stamp milling method (stone mill pestle milling method), a roll milling method, water grinding, and high-speed flour milling method (pin mill).
In particular, as a method for producing rice flour suitable for production of bread, cakes, noodles, and the like, for example, there is a method of producing rice flour using enzymes disclosed in Japanese Examined Patent Publication No. H7-100002 (hereinafter, Patent Document 1) or Japanese Patent No. 3076552 (hereinafter, Patent Document 2).
The method disclosed in Patent Document 1 is a method of, after immersing rice in a water solution in which pectinase (one of macerating enzymes) is dissolved, dehydrating and milling the rice, drying the rice to about moisture content of 15 weight % to prepare fine rice flour, heating the fine rice flour at temperature of about 150° C., and performing improvement of wettability and the like of the rice flour to enable use of the rice flour in a wheat flour use.
The method disclosed in Patent Document 2 is a method obtained by improving the method disclosed in Patent Document 1. This method is a method of selecting one or two or more kinds out of organic acid water solutions of sodium citrate, sodium lactate, sodium malate, sodium acetate, or the like mixed with pectinase to thereby create a treating solution and, after immersing rice in this treating solution, dehydrating, milling, and drying the rice.
Starch grain of the rice is compounded grains. A plurality of starch grains are included in amyloplast. The starch grains in rice grain albumen are tightly filled without a gap. A cell wall tissue wrapping the starch grain is firm. Therefore, in the case of a non-heated flour type, even if the rice is milled by the conventional method, only coarse flour can be produced. If the rice is ground by force, the starch grains are damaged. Both of processability and quality are markedly deteriorated.
Therefore, the methods disclosed in Patent Document 1 and Patent Document 2 provide a method of decomposing the cell wall tissue with the force of enzymes to thereby produce fine rice flour having round particles with a low starch damage rate.
However, although the method of producing rice flour using enzymes is an excellent method as explained above, the method has problems explained below.
That is, in the method of producing rice flour using enzymes, 0.05 to 0.1 weight % of enzymes are used with respect to 1 weight % of rice. A price of the enzymes is as high as 10,000 yen per 1 kg thus increases producing cost of rice flour.
For enzyme treatment, it is necessary not only to use a large quantity of water but also to provide a facility for treating wastewater after the use. Equipment cost and running cost for the facility are high and further increase producing cost of rice flour.
Furthermore, although the enzymes can be available in Japan, it is difficult to find such enzymes in overseas countries. Since the enzymes are living things, it is difficult to export the enzymes from Japan. Therefore, for example, in neighboring Korea or in South East Asian countries where a large quantity of rice is produced, rice flour cannot be produced using the enzymes.
Note that, as a method for producing rice flour, Japanese Examined Patent Publication H4-73979 discloses a technique for, after coarsely milling rice with a roll mill, milling the rice with an air mill to thereby obtain rice flour with less damage to starch grains. However, the rice flour obtained by the method has large surface roughness. That is, the surfaces of particles are angular. And, the angles crush fine air foam and the rice dough does not swell well. Therefore, as described in the section of “industrial applicability” of the publication, the rice flour obtained by the method is suitable for production of rice confectionery (rice crushers), dumplings, bean jam cakes, and the like. However, the rice flour is not suitable for production of bread, cakes, noodles, and the like.